The invention relates to pneumatic tires which have improved wet traction and wet stopping and handling characteristics.
Hydroplaning of tires on wet pavement has long been a problem in the art. A tire hydroplanes when running on wet pavement because the tire pushes water in front of it as it advances, until the backpressure of the water is sufficient to lift the tire off the road. The pressure of the water is a function of the depth of the water and the speed of the tire. Various tire designs, adapted to channel water away from the tire, and thereby maintain rubber contact with the road, have been tried by the prior art to correct this problem. Although prior art rain tire designs have improved wet traction, it is a continuing goal in the art to further improve wet traction.
Traction on wet pavement, i.e. pavement that is moistened as opposed to having standing water, known as QGL wet traction (Government standard xe2x80x9cQuality Grade Labelingxe2x80x9d), is also an important characteristic for a tire.
Often, a tire designed for hydroplaning characteristics has diminished QGL wet traction characteristics because of the low net to gross usually associated with tires designed for hydroplaning properties. Conversely, a tire with good QGL wet traction usually has diminished hydroplaning properties, because of the high net to gross associated with tires designed for QGL wet traction.
It is an object of the present invention to provide a pneumatic tire having improved wet traction, both for hydroplaning and QGL, while having good handling, wet stopping ability, and improved noise and improved wear and irregular wear characteristics.
Other objects of the invention will be apparent from the following description and claims.
xe2x80x9cAquachannelxe2x80x9d refers to an extra wide circumferential groove with angled (non parallel), rounded groove walls designed specifically to channel water out of the footprint contact patch of the tire.
xe2x80x9cBeadxe2x80x9d means that part of the tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards and chafers, to fit the design rim.
xe2x80x9cCarcassxe2x80x9d means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.
xe2x80x9cContact Patchxe2x80x9d refers to a section of footprint, in a footprint that is divided into sections by wide void areas, that maintains contact with the ground.
xe2x80x9cCrownxe2x80x9d refers to the circumferentially outermost portion of the carcass substantially within the width limits of the tread.
xe2x80x9cDesign rimxe2x80x9d means a rim having a specified configuration and width.
xe2x80x9cDirectional treadxe2x80x9d refers to a tread design which has a preferred direction of rotation in the forward direction of travel.
xe2x80x9cEquatorial plane (EP)xe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread.
xe2x80x9cFootprintxe2x80x9d means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under design load and pressure.
xe2x80x9cFootprint Net-to-grossxe2x80x9d refers to the actual footprint of a deflected tire and is the ratio of the ground contacting surface area of the tread to the total tread footprint area including the groove void area.
xe2x80x9cGroovexe2x80x9d means an elongated void area in a tread that may extend circumferentially or laterally about the tread in a straight, curved, or zig-zag manner. Grooves ordinarily remain open in the tire footprint. Circumferentially and laterally extending grooves sometimes have common portions and may be subclassified as xe2x80x9cwidexe2x80x9d or xe2x80x9cnarrowxe2x80x9d. Grooves may be of varying depths in a tire. If such narrow or wide grooves are of substantially reduced depth as compared to wide circumferential grooves which they interconnect, they are regarded as forming xe2x80x9ctie barsxe2x80x9d tending to maintain a rib-like character in the tread region involved.
xe2x80x9cLugsxe2x80x9d refer to discontinuous radial rows of tread rubber in direct contact with the road surface.
xe2x80x9cNet-to-grossxe2x80x9d refers to the ratio of the ground-contacting surface of a tread to the total tread area.
xe2x80x9cNormal load and inflation pressurexe2x80x9d refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the design rim and service condition for a tire of specific size. Examples of standards are the Tire and Rim Association Manual and the European Tire and Rim Technical Organization.
xe2x80x9cPneumatic tirexe2x80x9d means a laminated mechanical device of generally toroidal shape (usually an open-torus) having beads and a tread and made of rubber, chemicals, fabric and steel or other materials. When mounted on the wheel of a motor vehicle, the tire through its tread provides traction and contains the fluid that sustains the vehicle load.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d are used to mean directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cRibxe2x80x9d means a circumferentially extending strip of rubber on the tread which is defined by at least one circumferential xe2x80x9cwide groovexe2x80x9d and either a second such groove or a lateral edge of the tread, the strip of rubber being laterally undivided by full-depth narrow or wide grooves.
xe2x80x9cShoulderxe2x80x9d refers to the upper portion of sidewall just below the tread edge.
xe2x80x9cSidewallxe2x80x9d means that component which comprises a portion of the outside surface of a tire between the tread and the bead.
xe2x80x9cSipesxe2x80x9d refer to small slots molded into ribs of a tire that subdivide the tread surface and improves traction characteristics. Sipes tend to close completely in a tire footprint.
xe2x80x9cSlotsxe2x80x9d are elongated void areas formed by steel blades inserted into a cast or machined mold or tread ring. Slots ordinarily remain open in a tire footprint. In the appended drawings, slots are illustrated by single lines because they are so narrow.
xe2x80x9cTreadxe2x80x9d means a molded rubber component which, when bonded to a tire casing, includes that portion of the tire that comes into contact with the road when the tire is normally inflated and under normal load.
xe2x80x9cTread widthxe2x80x9d means the arc length of the road contacting tread surface in the axial direction, that is, in a plane parallel to the axis of rotation of the tire.
xe2x80x9cTurn-up plyxe2x80x9d refers to an end of a carcass ply that wraps around one bead only.
A pneumatic tire for use on paved surfaces comprises a pair of annular beads, and at least one carcass ply wrapped around the annular beads, a tread disposed over the at least one carcass ply in a crown area of the tire. Sidewalls are disposed over the carcass ply between the tread and the beads. The tread comprises a center rib, shoulder lugs and center lugs disposed between the shoulder lugs and the center rib. The tread has a footprint net-to-gross ratio of 60% to 68% and two annular aquachannels each having a width of about 10% to 12% (as measured from tangents on the curve of the aquachannel walls adjacent to the land area of the lug) of total tread width based on the design of the tire, and a depth of 90% to 100% of total tread depth, and two circumferential grooves each having a width of 3% to 5% of the tread width based on the design width of the tread.
The illustrated tire may be viewed as having a tread having two aqua-tread portions, each aqua-tread portion comprising an aquachannel disposed between two circumferential rows of lugs, wherein the width of the aquachannel comprises 15% to 25% of the width of each aqua-tread portion. In various embodiments of the invention, the aquachannel may be symmetrical in cross section, and the aqua-tread portions may be substantially symmetrical within said tread, or the aqua-tread portions may be different, which causes asymmetry within the tread. In the illustrated embodiment, the aquachannel comprises 20% to 24% of the width of each aqua-tread portion.
In one embodiment of the invention, the tire has a tread wherein the shoulder lateral grooves and the center lateral grooves are angled in the same direction.
In an alternative embodiment, the shoulder lateral grooves and the center lateral grooves are angled in opposed directions.
In an illustrated embodiment, the shoulder lateral grooves and the center lateral grooves are angled in the same direction and have the same angle with respect to the EP of the tire on both sides of the center rib, the center lateral grooves are not continuous with the shoulder lateral grooves, and the aquachannels separate the shoulder lugs from the center lugs.
Also in an illustrated embodiment, the shoulder lugs are continuous with center lugs in a minimal tread depth within the aquachannel.
Other embodiments may comprise tires in which the tread pattern is directional, or the tread pattern is non-directional, or the tread has different rubber compositions axially disposed in different circumferential zones of the tire, or the tread comprises a blend of a rubber composition showing good treadwear and a rubber composition showing good traction.
In the illustrated embodiment, the tire has circumferential reinforcement comprising high tensile steel wire and a footprint factor of 1.05 to 1.25 wherein the footprint is wider than it is long, and the tire has an apex extending substantially to the midsection height of the tire.